Emergency service transmission, for example, transmission of some alarm information in industrial control, is an application scenario in future 4.5G and 5G communications systems. For an emergency service, a small volume of data needs to be fast transmitted each time. A short transmission delay is an important feature of the emergency service.
In the prior art, when a base station sends a non-emergency service, to be specific, a conventional data service in an existing communications system, for example, a mobile broadband (MBB) service, to user equipment (UE), because a system resource in a current TTI has been allocated and occupied, the base station usually needs to wait for a next transmission time interval (TTI) or even a longer time to obtain an idle resource, and finally sends the downlink service by using the idle resource. The downlink service sending method in the prior art has low efficiency. If the prior art is used to transmit a downlink emergency service, a delay occurs in transmission of the downlink emergency service, and the UE cannot process the downlink emergency service in time.